Using Facebook's general privacy settings (find these by hitting "account" on the top right of a Facebook page) you can select whether everyone, just friends or friends of friends can see your status updates. However, there is a way to narrow those options down even further.
You can select specific friend lists to see your status (relevant for work, special interest groups, etc.) or even individual people by name, which is useful for anyone organizing a surprise party.
To take advantage of these options, click the padlock icon just below your "what's on your mind" box on your wall and a drop down menu should appear. Selecting "customize" will bring up more options such as "make this visible to" and "hide from" with the option to make your selection a default.